Semibright nickel deposition



"semi bright or blushed.

Patented Feb. 24, 1-942 orrlca snmnarcnrm'cxan DEPOSITION Andrew Wesley, Plainfield, N. J., and Jay William Carey, Lynbrook, N. Y., assignors to The International Nickel Company, Inc., New.York,

N. 1., acorporation of Delaware Application December 29, 1938, Serial No. 248,146

'6 Claims. (01. 204-49) The present invention relates to a process of producing semi-bright deposits of nickel, and more particularly to a process of .producing semibrightdeposits of nickel by using an electroplating bath consisting principally or preferably substantially entirely of an aqueous solutionvof nickel chloride and boric acid in critical amounts under properly correlated critical conditions of tern perature, current density and hydrogen ion concentration, and in the absence of brightening addition agents."

Nickel deposits produced by ordinary commercial practice have been matte or dull in appearance, requiring expensive polishing and bufling operations to produce the desired bright appearance. In order to avoid the expense and disadvantages inherent in such prior art practice many attempts have been made to produce nickel coatings which were so smooth that no, or only slight, bufflng was required to bring out a high luster. Coatings which gave a specular reflection without bumng were known in the art as. bright" whereas those which had the appearance of a mirrored surface thathad been breathed upon and which required only slight bumng to produce a bright or mirror-like finish were designated The art in recent years has attempted to produce bright and semibright deposits by the use of brightening addition'agents in the electroplating bath. Theseagents were, generally speaking, additions of organic or inorganic materials such as sulfonated naphthalene or terpene compounds, albumins,

cadmium salts and lead salts intended to give bright or semi-bright deposits directly in the bath; Even with the most recent improvements, this art suffered from several disadvantages which limited the commercial usefulness of baths containing brightening addition agents. The chief disadvantage was the dimculty of maintaining the bath composition constant over a period of time. The brightening addition agents were not perfectly stable and were difficult to maintain in constant concentration in the bath. So much highly skilled technical service had to be given to users of such baths that none of them was in widespread. use in smaller plating shops. Other shortness of the deposit; a pronounced tendency for development of pits in the deposit and with.

some plating baths the permissible variation in plating conditions such as temperature and current density was very narrow.

, comings of these processes were extreme brittleand 0! getting coatings of nickel free from pits; it was common practice to use multiple coatings of nickel and copper and to confine the polishing operations to the copper "layer. Moreover, experts in the art advised against the use of a nickel chloride bath for depositing nickel directly on iron due to the poorbond formed between the coating and the iron which resulted inthe plating peeling oil a short time'after deposition.

There was a definite and-well recognized need in the art for a method of depositing single layer coatings of nickel free from pits and smooth enough to buff easily and which was not subject to the operating 'diiiiculties mentioned hereinabove.

We have invented a process of electrodeposlting nickel free from pits and in such smooth form that a high luster can be developed by slight buffing. In our novel and improved process an easily controlled electroplating solution composed substantially entirely of an aqueous solution of nickel chloride and boric acid in critical amounts is used and the plating conditions in-' cluding the hydrogen ion concentration, temperature and current density are controlled within critical limits properly correlated with the bath composition to produce satisfactory and ac' ceptable semi-bright nickel deposits.

It is an objector the present invention to provide a process of producing semi-bright coatings of nickel which may be brought to a high luster with only slight bufing.

It is another object of the present invention to provide a process of producing semi-bright deposits of nickel by the use of a readily controllable electroplating bath capable of wide commercial use even in smaller plating shops where highly skilled technical service cannot practically be given.

It is a further object of the present inventionto provide a process of producing semi-bright single layer coatings of nickel on other metals such as iron, steel, brass, etc., in which the plating conditions including hydrogen ion concen: ,tration, temperature and current density may be varied within relatively wide but critical limits by proper correlation with each other and with the bath composition. I

The invention also contemplates a process of producing relatively thick coatings of electrodeposited nickel free from pits and excessive brittleness and which are so smooth that they maybe brought to a high luster with slight b.

Other objects and-advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings in which:

bath containing principally nickel chloride and boric acid in aqueous solution without brightening addition agents," and by properly correlating hydrogen ion'concentration, current density and temperature within critical limits, as hereinafter described. The present invention makes it possible to produce directly thick deposits of semi-bright nickel so smooth that they require only slight bufling to be brought to a high luster. At the same time the deposits are satisfactory in respect to adherence, ductility, soundness and freedom from pits. The extreme simplicity of composition of the plating bath and the relatively wide range of'permissible variation in plating conditions within critical limits make this process unusually easy to control. The process of the present invention, moreover, may be used to plate nickel directly on iron or steel, and the nickel plating so produced adheres well and has no tendency to peel off.

In the plating bath employed in the present invention, critical amounts of nickel chloride and boric acid are dissolved in water. Preferably the bath contains about 300 grams per liter of nickel chloride and about 30 grams per liter of boric acid. No addition of brightening agents of any kind need be made to the present improved bath to obtain the desired semi-bright nickel deposits. The boric acid content may vary from more than about 35 grams per liter down to less than about grams per liter. Satisfactory results may be obtained provided more than a critical minimum content of boric acid is present which is designatd by the curve A in Fig. 1. The abscissa in this graph represents borlc acid concentration and the ordinate the nickel chloride concentration of the bath, both in grams per liter. If boric acid is present in an amount less than that depicted, the nickel deposit is burned and unsatisfactory. Beyond about 35 grams of boric acid per liter, the solubility of boric acid at room temperature is exceeded and flakes of boric acid settle out when the bath is allowed to cool. About 35 grams of boric acid per liter represents a practical -maximum for commercial and industrial operations but the present invention is not limited to this amount as an absolute maximum. Satisfactory results may still be obtained when the boric acid concentration is substantially saturatedat the operating temperature. While the theoretical function or functions of boric acid in its unique cooperation and combination with nickel chloride in the bath are not thoroughly understood, it is believed that boric acid does serve to bufler the solution. Curves B and C indicate minimum and maximum contents" of nickel chloride in the form of NiC12.6HzO. Between the limits of about 260 grams and about 340 grams of NiC12.6H2O per liter satisfactory semi-bright deposits are obtained. Either above or below these i itical limits, matte deposits are formed. The curves in Fig. 1 were determined with a bath temperature of 100 F., a pH of 1.0 and a current density of '75 amperes per square foot, but the positions of the curves do not change substantially with varying plating conditions within the limits hereinafter set forth.

The acidity limits for producing satisfactory semi-bright deposits with the nickel chlorideboric acid bath are defined by about pH=0.'7 and about pH=3.0. The pH is maintained by additions of hydrochloric acid instead of the customary sulfuric acid. These limits are critical. Numerous experiments have demonstrated that satisfactory semi-bright deposits cannot be obtained with the above mentioned bath unless the pH value is less than 3.0. Below a pH of about 0.7, the cathode current efliciency becomes too low for satisfactory commercial operation.

Bath temperature and current density must be coordinated with each other and with the hydrogen ion concentration in order to obtain the desired semi-bright deposit of nickel. These relationships are depicted graphically in Figs. 2, 3 and 4 in which the abscissa represents current density in amperes per square foot, and the ordinate is temperature in degrees Fahrenheit.

The bath employed for each series of tests contained about 300 grams per liter of NiCl2.6H2O and about 30 grams per liter of boric acid with the pH and other plating conditions controlled as hereinafter set forth.

In one series of tests, a constant pH of about 0.75 was maintained while current density and bath temperature were varied. Current densities from very low values to more than 200 amperes per square foot were found to produce satisfactory semi-bright nickel deposits provided the bathtemperature did not rise above a critical value indicated by the curve D in Fig. 2. Below the curve D satisfactory semi-bright deposits were obtained, but above the curve the deposits were matte.

The pH value was maintained at about 1.0 for a second series of tests in which both temperature and current density were varied. Within the area defined by curves E and F in Fig. 3.

. satisfactory semi-bright deposits were produced.

When. the temperature lay above curve E at any particular current density the deposit wa matte.

Below curve F, the deposit is burned and unsatisfactory.

In Fig. 4, the results are plotted of a third series of tests conducted at a pH of about 2.0 The area between the curves G and H represents the conditions of temperature and current density which yield satisfactory semi-bright nickel deposits. Above curve G and below curve H the deposits are matte and burned respectively as described in connection with Fig. 3.

It will be seen from a study of Figs. 2, 3 and 4 that the area defining the ranges of permissible temperatures and current densities decreases progressively as the pH rises. A fourth seriesoi tests conducted at pH=3.0 demonstrated that the area had substantially disappeared.

While the operable range of pH is about 0.7 to

preferably be so correlated as to fall well within the semi-bright areas oi Figs. 2, 3 and 4. I

It will beunderstood by those skilled in the art that lines of curves D, E, F, G and H actually represent areas of somewhat'varying width. In other words, for any given current density and pH, e. g., 140 amperes ,persquare foot and pH=1,

the deposit does not suddenly change from semibrig'ht to matte with a slight temperature change,

-e. g., from slightly less to slightly more than 141 F. (see Fig. 3) On the contrary, there is a relatively narrow temperature range over which the deposit changes rather rapidly from semibright to matte.

The following specific example is illustrative of the results that may be obtained by practicing the present invention.

An aqueous plating bath was prepared having the following composition:

NiC12.6I-I2O about 300 grams per liter H3303 about grams per liter Sufllcient hydrochloric acid was added to the aqueous solution to adjust the pH to about 1.0.

A bagged, rolled, depolarized nickel anode was used and the'solution was filtered continuously. Slight agitation oi the bath was obtained by means of a gentle stream of air. The bath temperature was maintained at about 110 F. while a steel object was coated directly with nickel at a cathode current density of about 75 amperes per square foot. After about 19 minutes a semibright deposit about 0.001 inch thick had been formedwhich was brought to a high flnish'in a single bufling operation using asoft rag wheel treated with an ordinary grease coloring compound containing rouge. A bright, mirror-like surface was .obtained at agiven point'in about 10 seconds.,

The art recognizes three-general classes of nickel plating: viz., the ordinary white nickel,

'bright nickel and semi-bright or blushed nickel.

The term white nickel has been used to describe the color of matte deposits and has no reference to any degree of brightness. A

is difluse reflection. A "semi-brigh deposit is one approaching the smoothness oi a bright de posit but falling somewhat short oi a specular reflection of incident light. It appears like a mirror that has lust been lightly breathed on. The terms "blushed and milkyfare also used to describe semi-bright deposits. Enough-light is reflected specularly thatimages or objects can spectrometer-table and in a plane normal to the table. It was illuminated by a thin collimated beam oi white light of about 1500 foot candles intensity, incident upon the specimen at a known angle .with i espect to the surface of the specimen. The light emitted directly back from the specimen was then reflected from the surface of a thin cover glass, placed at to its path, toward an illuminometer which was used to measure they intensity of the reflected beam in apparent toot candles. By inclining the specimen at various angles to the incident beam, data for curves correlating the angle of incidence (which in this procedure is the same as the angle 0! reflection) and the intensity of the reflected light was obtained. i

These data for typical matte. semi-bright and bright specimens with coatings 0.001 inch thick are plotted in curves I, J and K of Figure 5 which .involve quite different magnitudes and distributions of intensities for the different types of deposit. Almost all of the light reflected from a truly bright nickel deposit is reflected in one direction and the maximum intensity observed is at least about or more of the intensity of the incident light- (See curve K.) Typical semi-' bright or blushed deposits are characterized by one or more peaks in the curve with a maximum observed intensitly within the range of about 80 to about 600 foot candles when the incident light has an intensity of about 1500 foot candles, i. e.. the reflected light is about 2 to 40% of the incident light. (See curve 5.) Typical matte de-v posits, however, reflect light of less than 20 toot candles intensity under comparable conditions over a wide range of angles of incidence and refiection', i. e., about 1.5% or less. curve I.) It will be apparent from theioregoing that the present invention provides a practicable and satistactory process oi. producing semi-brmht nickel deposits. The bath is relatively inexpensive, easy to make up and maintain, and is stable. For example, a bath oi the type described hereinbefore "has been operated for the purposes 0! testing over a period of years depositing semi-bright nickel on a great number of steel test pieces during that time. At the end of the period, the bath produced 7 just as good semi-bright nickel deposits as'at the be distinguished at fairly small angles of incidence, albeit not very clearly and with hazy, instead of sharp, edges. l 1

In order to deflne more precisely the diflerence between matte, semi-bright and bright deposits,

results of brightness measurements made by the method originated by P. Bouger [Trait d'O'ptique'sur la Gradation de la Lumiere, Paris, Guerin and Delatour (1760) 1 have been plotted in Fig. 5. Inperforming these measurements, .the specimen, in the form of a flatrectangular piece of steel sheet coated with a nickel deposit about 0.001 inch thick, was placed at the center 01} a beginning. Although the nickel-was depositeddirectly on the steel foundation metal, it adhered strongly thereto and did not peel off even when exposed for long periods to the atmosphere. Slight buffing, for, example, with a rag bumng wheel and ordinary rouge bufling compound forabout 10 sec'ondaproduced a bright. mirror-like flnishat any particular spot. Deposits as thick as about 0.008 inch may readily beobtained by the process embodying our invention which are still semi-bright and readily polished with slight:

buiiing to bright, mirror-like finish.

We claimz' 1. A plating bath consisting oi. anaqueous so- V lution containing nickel chloride within the range of about 280 to about 340 grams per liter, boric acid from about2 grams per liter to saturation at the bath operating temperature, and au'flicient hydrochloric acid to regulatev the pH about 0.7 and 3.0.

2. A. process of electrodepositing adherent.

semi-bright coatings of nickel on a foundation metal comprising establishing an aqueous plating bath consistingprin'clpally 0! about 200 to 840 grams per liter of nickel chloride and from about 2 grams-to about 35 grams per liter of boric acid. adjusting the pH value of thebath between about between 0.7 and less than 3 by additions of hydrochloric acid, heating the bath to a temperature or about 80 F. to about 145 F., and depositing nickel upon I a foundation metal at a current density of about 20 to about 200 amperes per square foot to produce a semi-bright adherent coating of electrodeposited nickel on the foundation metal.

3. A process of electrodepositing adherent, semi-bright coatings of nickel on a foundation metal comprising establishing an aqueous plating bath consisting principally of about 260 to 340 grams per liter of nickel chloride and from. about 2 grams to about 35 grams per liter of boric acid, adjusting the pH value of the bath between about 0.7 and less than 3 by additions of hydrochloric acid, heating the bath to a temperature of about 80 to l 45 F., making a piece of foundation metal to be plated a cathode in said bath, and depositing nickel thereon at a current density within the semi-bright areas represented by the curves of Figures 2, 3 and 4 for the particular temperature of the bath.

4. A plating bath consisting of an aqueous solution containing about 300 grams of nickel chloride per liter, about grams of boric acid per liter and sufficient hydrochloric acid to regulate the pH between about 0.7 and about 3.0

5. An aqueous nickel electropating bath consisting principally of an aqueous solution of about 260 to about 340 grams of nickel chloride per liter, about 5 to about grams of boric acid per liter and sufflcient hydrochloric acid to provide a pH of about 0.7 to about 3.0.

6. A process for depositing adherent electrodeposits or nickel directly upon a ferrous base metal which comprises electro-depositing nickel from an aqueous plating bath consisting principally of about-260 to about 340 grams per liter of nickel chloride and from about 5, grams to about 35 grams per liter of boric acid, adjusting the pH value of the bath between about 0.7 and less than 3 by additions of hydrochloric acid, heating the bath to a temperature of about F.

'to about F. and depositing nickel upon said ferrous base metal at a current density of about 20 to about 240 amperes per square foot to produce a semi-bright adherent coating of electrodeposited nickel on the aforesaid ferrous base metal.

ANDREW WESLEY.

JAY WILLIAM CAREY. 

